1. Field of the Invention
The present invention as directed to a method and a device for acceptance and stability testing of filmless dental radiographic equipment.
2. Description of the Prior Art
German OS 36 42 565 discloses for the purpose of stability testing of dental radiographic equipment which is operated in conjunction with an X-ray film a device which comprises a test body having a radiation-absorbing staircase made from a plurality of elements of different absorbing capacity. A depression into which an X-ray film can be inserted is located in the test body. The test device can be mounted on the tube of radiographic equipment and holds a centring aid suitable for this purpose.
Furthermore, U.S. Pat. No. 4,352,020 discloses a computed tomography apparatus in which for the purpose of stability testing of the characteristic properties of detectors it is possible for a multiplicity of so-called phantom elements of different absorptive capacity to be brought into the beam path of the X-ray source. In order to establish deviations of the detectors, radiation is applied to the latter, once without and after with phantom elements inserted into the beam path. The comparative values thus obtained are evaluated in a computing unit and displayed on a display.
In the case of filmless dental radiographic equipment, in which the X-ray radiograph is recorded by a sensor, for example a CCD sensor, the need exists, as in the case of the present day X-ray film technology to submit the sensor to checking, specifically once during acceptance of the equipment and later at regular intervals. In the case of the (stability) test to be provided at regular intervals, which is usually carried out by the operator of the radiographic equipment, it can be concluded whether the radiograph-producing system has remained stable within fixed limiting deviations.
An object of the present invention is to specify a test method tuned to such filmless dental radiographic equipment.
The above object is achieved in accordance with the principles of the present invention in a method and an apparatus for acceptance and stability testing of filmless dental radiographic equipment wherein a test measurement body having a number of absorption elements with respectively different radiation absorption characteristics is disposed in the beam path of incoming x-rays at a defined close proximity from a radiation sensor, and wherein electrical signals obtained from the sensor due to the radiation incident thereon are supplied to a computing unit which processes these signals to form image value signals, and wherein the image value signals are fed either directly to an output unit, such as a monitor or a printer, or are first compared with prescribed desired image values and, in the case of deviations from the prescribed values, the deviating values are supplied to the output unit.
An advantage of the invention is that the inventive method and apparatus permit computer-aided analysis of the measurement results. A subjective, visual assessment can be further supported or supplemented thereby.
The method proposed according to the invention can be applied both to dental radiographic equipment having sensors which can be placed intraorally and to dental radiographic equipment by means of which panoramic tomographs or remote X-ray images can be made. Accordingly, the test measurement body can be advantageously configured in such a way that it is suitable both for reproducibly holding a sensor which can be applied intraorally and for holding on the secondary diaphragm of a panoramic tomographic camera.
In application with equipment having a sensor which can be applied intraorally, it is advantageous to fit the test measurement body with a sensor holder which permits the sensor to be held at a close defined distance, for example of a few millimeters, from the edge of the tube and to be rotated advantageously about the axis of the tube in specific angular degree steps. The sensor holder fixes the sensor at the prescribed distance relative to the center of rotation.